This invention relates to a hydraulic power and control system for an industrial machine, such as a hydraulically powered excavator or the like.
Hydraulic excavators conventionally utilize hydraulic cylinders to control the position of the main excavator boom, to control the position of the arm at the end of the boom, and to control the position of the bucket at the end of the arm. Also, a hydraulic motor is conventionally utilized to rotate the excavator body that carries the boom on the undercarriage and it is also known to use a pair of independently controlled hydraulic motors to drive the opposite tracks of the machine's undercarriage to propel and steer the machine. Typically, such hydraulic systems have been open center type systems.
Generally, when such excavators are operating, the throttle of the engine is set at a relatively high level to provide a high level of power for the machine. However, such machines are frequently in a condition where none of the hydraulic functions on the machine are being operated at that particular moment. For example, when the machine is loading trucks, there is normally an interval between the time when one truck is loaded and the next truck is positioned for loading. Obviously, it is inefficient to operate the engine at a high level when the excavator is in an idled condition.
Accordingly, it is known to provide some type of automatic throttle back control to automatically throttle back the engine a predetermined time delay after operation of the hydraulic function ceases. One system of this type has featured sensors to pick up the position of the control levers for the valves that control the hydraulic functions, such as the swing position of the excavator, or the cylinders that control the positions of the excavator boom, arm, or bucket. However, such a system is necessarily relatively complex.